A TUGBOAT that disconnected from the Transocean Winner oil rig during a severe storm in the Western Isles has been left at Stornoway port a week after it was battered off the west coast of the Isle of Lewis.

The Sunday Herald has learned that the towline has been left in the port at the same time as Marine Accident Investigation Branch (MAIB) officials are conducting a probe into the grounding.

Last night, a port works keeper at Stornoway who asked not to be identified, said: “It’s been in the harbour here for days and it’s a small harbour. I’ve no idea what’s happening to if though.”

The Transocean Winner was carrying 280 tonnes of diesel – more than 300,000 litres – when it was blown ashore early on Monday after its towline detached from the tug Alp Forward. The rig was being towed from Norway to Malta, and was subsequently due to be scrapped in Turkey.

It is now thought to have leaked more than 50,000 litres of diesel.

However, a spokesman for the Dutch-based tug owners ALP Maritime refused to speak about the potential cause of the grounding, and said it was not appropriate to speculate about any potential financial losses the firm would face.

They said: “So far we know the towline broke during a severe storm and the severe weather conditions did not allow for a new towline to be reconnected to the Transocean Winner.

“With the MAIB investigations currently underway we believe it’s not appropriate to make any firm statements on the root cause.

“As we’re still in an assessment phase it’s also too early to say anything about potential losses.”

Last night the MAIB confirmed its investigation team had now left the site where the 17,000-tonne rig was swept ashore.

An MAIB spokesperson said the results of the investigation would be published in “due course”, but refused to give details of any lines of inquiry.

The MAIB would not state whether its officials would return to the site this week to pursue their investigation, which the body’s website says is into the “grounding of a semi-submersible on the west coast of Lewis after it became detached from the tug Alp Forward”.

Meanwhile, industry body Oil & Gas UK said it was closely monitoring the affected area, as it called for lessons to be learned from the incident.

Mick Borwell, its health, safety and environment director said: “Oil & Gas UK has closely monitored the situation involving the stranded oil rig in Lewis and we will continue to do so, as safety and the environment are of paramount importance to our industry.

“Oil & Gas UK works to share best practice across the sector and we will ensure any lessons are learned from this incident.

“We recognise that a vessel with suitable towing capabilities, which can be deployed to support HM Coastguard in the event of an emergency incident, plays an important role, in particular where there is a threat of pollution.”

The MAIB probe came as plans to airlift a salvage team on to the grounded rig had to be abandoned because of bad weather.

Maritime and Coastguard Agency (MCA) officials said conditions were unsuitable to winch the team of eight safely down to the rig, on Dalmore beach near the village of Carloway.

Rig owner Transocean and a team from Netherlands-based Smit Salvage are considering bringing in additional aircraft to help airlift the team on board, which is impossible from the sea.

The MCA said it had been hoped the salvage team would be able to carry out a further damage assessment and inspect the emergency generator to establish what power was available.

Meanwhile, Western Isles Council said a “low level” of pollution had been detected by tests, but daily shoreline inspections by the Scottish Environment Protection Agency had indicated no visible sign of pollution.

No-one was on board the rig when it ran aground and people are being urged to stay away from the beach.

The Transocean Winner has a fuel oil capacity of 21,495 barrels and has enough accommodation for 108 people. It was built in 1983 and underwent significant upgrades in 2006.